The present invention relates to a method and apparatus for removing debris from the surface of a rotating drum, and more particularly it relates to a method and apparatus for removing polymeric degradation products and other materials from the surfaces of plastic bag making machinery.
In the production of individual flexible web products such as plastic bags and containers, the bag stock is typically supplied in the form of a continuous web of thermoplastic material which has been folded upon itself to form two plies. In forming individual plastic bags and containers, portions of the thermoplastic material are severed from the web. These severed areas also become side seams for the bags because they are typically sealed at the same time as they are severed by the use of a heated wire element. The plastic bags are then stacked, counted, and packaged by packing equipment.
The severing and sealing operation typically takes place on a relatively large diameter rotating drum, known as a seal or product drum, which may contain multiple heated wire severing and sealing elements positioned in grooves located within the outer periphery of the drum. As the drum rotates, different severing and sealing elements are actuated to raise them up to the drum surface to sever and seal a respective portion of the web of bag stock. Such heated wire severing and sealing elements are typically maintained at temperatures ranging from 1000.degree. F. to 1300.degree. F. or higher. The individual bags are retained on the drum by a vacuum arrangement as the drum rotates.
Individual bags are then taken from the drum, stacked, and packaged. Presently, individual bags are taken from the drum by a smaller drum, known as a transfer drum, also suitably equipped with vacuum capabilities. The vacuum on the bags on the product drum is relieved at an appropriate point, and the bags are pulled onto the transfer drum and held in position there by vacuum. At an appropriate point, the vacuum is released and the individual bags are pulled off the transfer drum by an orbital packer or similar device.
During the severing and sealing process, a portion of the polymeric bag stock is pyrolized, resulting in the formation of both airborne and melted polymeric particles and polymeric degradation products. The melted polymeric particles and condensed airborne polymeric particles accumulate upon the surface of the product drum, transfer drum, and related machinery to form an ever increasing buildup. As will be appreciated, this polymeric build-up creates substantial operational problems and can affect product quality.
A first problem is that the machinery surfaces may transfer the polymeric material and degradation products to the bag stock being handled, thereby contributing to odor and off-taste in any food which may be later stored therein. In addition, accumulations of the polymeric materials and degradation products on the product and transfer drums clog the vacuum ports thereon, leading to improper bag transfer between the product and transfer drums, as well as resulting in product and equipment jamming. Moreover, such accumulations on the transfer drum in particular induces poor product packaging and frequently causes the packaging equipment which removes individual bags from the transfer drum to jam and otherwise operate improperly.
Presently, the bag making equipment must be shut down frequently and their surfaces cleaned to alleviate product and equipment jams and to rectify packaging malfunctions caused by accumulations of polymeric materials and degradation products on the machinery. Such shut downs are costly both in terms of maintenance expense and in terms of lost production. In addition, poor packaging results in the costly rejection of a substantial percentage of the finished product. Furthermore, the polymeric build-up results in a high degree of inconvenience to the operators of the bag making equipment who are forced to continually cope with the operational and product problems caused by the build-up.
Although the bag making equipment can be shut down and thoroughly cleaned, it is desired to provide a means for continually removing debris from the equipment while the equipment is in operation. Such means would reduce down-time, improve operational and product quality, and minimize rejected product due to poor packaging. Present methods and devices for continuous cleaning of rotating cylinder surfaces in other arts generally provide a cleaning cloth pressed against a cylinder whereby the cleaning cloth is continuously supplied by a supply roll and taken up by a takeup roll.
In U.S. Pat. No. 4,953,252 to Akisawa, for example, a cleaning material strip is fed out from a feed-out roll and is taken up by a takeup roll. Between the feed-out roll and takeup roll, the cleaning material strip is pressed against a roll surface to be cleaned by a pressing mechanism to capture dirt on the roll surface. The cleaning material strip is continuously advanced in a direction counter to the rotation of the roll to be cleaned. Vibration and sucking mechanisms to enhance dirt removal are also disclosed.
U.S. Pat. No. 4,110,035 to Kamata discloses a supply spool and a takeup spool for advancing a web against a photoconductive surface to be cleaned. The web is pressed against the photoconductive surface by a pressure member. A blade is provided to scrape the web from the pressure member to prevent the web from winding around the pressure member.
U.S. Pat. No. 4,757,763 to MacPhee et al. discloses a cleaning cloth supply roller for providing a cleaning cloth to a take-up roll. The cloth is advanced and pressed into contact with a printing blanket cylinder by an inflatable bladder for cleaning the cylinder during the cleaning cycle.
U.S. Pat. No. 4,867,064 to Hara et al. discloses supply and take-up rolls for advancing a cleaning cloth against the direction of rotation of a printing cylinder. A plenum chamber expands to bring the cleaning cloth into contact with the printing cylinder.
Such prior art devices have the disadvantage of occupying a great deal of space in the vicinity of the surface to be cleaned due to the necessity of requiring both a supply and a take-up roll as well as requiring means to press the cleaning cloth into contact with the surface to be cleaned. Such devices have proven to be too large and cumbersome to be used with bag making machines. Due to the number, size, and orientation of the peripheral pieces of equipment which are used in conjunction with bag making machinery (see, e.g., Smith et al. U.S. Pat. Nos. 4,911,423 and 4,919,415) very little space is left for a continuous cleaning device. Such limited space simply does not permit the utilization of the large prior art cleaning devices for the removal of polymeric debris from the surface of the machinery. In addition, while the bag making machinery is in operation, the operator must be permitted to have a clear view of the machinery in order to determine whether adjustments must be made. The cylinder cleaners of the prior art unacceptably block visibility of the bag making machinery due to the amount of space which they occupy.
Another problem with prior art cylinder cleaners concerns accessibility to the bag making machinery. The few unoccupied spaces around the machinery are strategically situated to provide access thereto for any maintenance or adjustments that become necessary. Any continuous cleaner placed in these spaces must be small enough and/or removable to permit access to the bag making equipment. The size, configuration, and immobility of the prior art cleaning devices do not allow such access.
Replacing the cleaning cloth presents an additional problem inherent with the prior art cleaning devices. When the cloth on the feed-out roll has been expended, the used cloth must be removed from the take-up roll, new cloth must be installed on the feed-out roll, and the new cloth must be fed through the cleaning device and attached to the take-up roll. Such a process is difficult and time consuming, further exacerbating production losses due to downtime.
Accordingly, it would be desirable to be able to continuously clean the surfaces of bag making machinery such that the means for cleaning the machinery would easily fit into the available spaces around the machinery to allow for a clear view thereof and physical access thereto. Additionally, the means for cleaning desirably would have a cleaning surface which is quickly and easily changeable. The need still exists in the art for such a method and apparatus for removing polymeric materials and polymeric degradation products from the surfaces of plastic bag making equipment.